z'ing and bagging a 64 Longbed, what would be better?

[ElkyRacer]

Ive got a 64 Longbed Im going to start gathering parts to z/notch and bag. Ive got a buddy with a pair of McGaughys 67-70 2.5 drop spindles I can pick up for cheap. What would be better here. I know where to find a whole crossmember/a-arms/ect for a 67-70. I can also pick up a newer 85 model front, and buy drop spindles for it. Which would be better? Did they drasticly change the caster/camber values in the 80s trucks? Would this be a better handling setup? This truck will eventually have a motor weighing right around a BBC, and the truck will be used for car hauling. Would the older stuff be up to the task? Or should I ditch the stock stuff/6lug and go with the newer 80s stuff with 5 lug?
And after all is said and done, when I take it to get aligned, what specs should they align it to. Any special stuff needed to be changed for a lowered truck like this?

Thanks for all your help guys.
Kyle